The present invention relates to a permanent magnet synchronous motor and a compressor and a rotor using the same.
An advantage of an induction motor is that, because it has a sturdy structure and is capable of line starting with a commercial power supply, it can be configured at low cost as a driving source of a machine of a constant speed drive which does not require speed control.
A synchronous motor can configure a drive portion at low cost as with the induction motor, and besides, there is almost no secondary copper loss in steady operation so that it has a merit of greatly contributing to improvement in efficiency of a drive system as compared with the induction motor. As its drawback, however, it has a cage winding for starting on a peripheral side of the rotor and it is necessary to further place permanent magnets on an inner peripheral side of this cage conductor so that the space for a layout of magnets is limited. Consequently, there are problems in terms of design, such as increase in leakage fluxes between magnetic poles and difficulty in rendering an induced electromotive force waveform as a sine wave.
As for a method of deciding the layout of permanent magnets to be embedded in the rotor, there are the techniques disclosed in JP-A-2005-117771, JP-A-2002-369422 and the like. They aim at optimization of the number of magnetic poles and structure of the synchronous motor for applications as systems such as a compressor and an electric vehicle respectively.
In the case of designing a self-starting permanent magnet synchronous motor for the compressor with the conventional techniques, there is concern that an excessive magnet amount may increase iron loss and input currents due to field weakening in steady operation and braking torque which blocks starting torque necessary for self-starting while an insufficient magnet amount may cause shortage of induced electromotive force for generating a desired output. In the latter case, it often leads to characteristic degradation such as increase in currents and reduction in power factor in conjunction with occurrence of magnetization.
An object of the present invention is to provide a permanent magnet synchronous motor with a rotor structure capable of improving motor efficiency without increasing iron loss and input currents in steady operation and braking torque on starting, a rotor thereof and a compressor using the same.